1. Field of the Invention
This invention generally relates to binoculars and, more particularly, to low-cost, light-weight, compact binoculars with adjustable interpupillary distance.
2. Description of the Prior Art
Dual-path optical systems are well-known in the optical arts and include two general classes of devices, binoculars and bioculars. Binocular devices include any instrument in which both eyes are used to view an image to achieve stereoscopic effects or to facilitate observation. They are characterized by having two mechanically linked, but optically uncoupled optical paths, to provide separate twin inputs and outputs to the visual system. True stereoscopic perspective is, more or less, commonly present in such devices so that an observer sees objects from slightly different points of view to permit the perception of depth and dimension. Prism binoculars, binocular magnifiers, and binocular microscopes are examples of such systems.
The most common biocular devices are those which are designed so that both eyes view an object through a single exit pupil, i.e., there is a single input and a twin output. They are different from binocular devices in that they contain elements that are common to both eyes. Examples of such devices include gunsights and general purpose night vision goggles such as those described in U.S. Pat. No. 4,392,710.
In both binocular and biocular devices proper image orientation and stereoscopic perspective is normally desired and achieved through the use of elaborate erecting systems in conjunction with suitable objectives and eyepieces. For example, the erecting system commonly used in standard binoculars to achieve the stereoscopic effect and proper image orientation comprises double Porto prisms in conjunction with modified Erfle eyepieces and achromatic doublet objectives. Such systems are more or less expensive and difficult to fabricate because of the tolerances required in manufacture and alignment of the various components, especially the prisms, where angular errors can be introduced at each surface.
The spectrum of known binoculars ranges from the very expensive to the very inexpensive. Prices can range from several hundred or more to under ten dollars. The high price end is represented by those which use high quality optical components that are complex in design, fabrication and testing. Such instruments are for the observer who requires excellent performance in light gathering, resolution, magnification and field coverage. They tend to be heavy to moderately heavy owing to the use of large glass components and thus are not convenient to transport. At the low end are those based on marginal designs which are made of the lowest quality components that are assembled with little care for attention to detail, quality, and performance. This class of binocular has limited utility especially where image quality is a concern, and therefore, has little value to offer. At modest prices, say under one-hundred dollars or so, there is a class of binocular that is quite good in performance and convenience. This class of binocular is quite valuable but still is not something that most people would tend to carry with them unless they specifically plan on their use. Consequently, there is a need for a binocular that may be retailed to a large segment of the population for use at popular attractions such as theater, concert, and sporting events, and it is a primary object of this invention to provide such binoculars.
It is another object of the present invention to provide low-cost, compact, and light-weight binoculars that can be adjusted to match the range of interpupillary distances of intended users.
Another object of the present invention is to provide a low-cost binocular system that can have interpupillary distance adjusted by a simple sliding action.
Yet another object of the present invention is to provide a low-cost binocular system that has a rectangular field of view and an adjustable interpupillary distance.
Still another object of the present invention is to provide a low-cost binocular system that folds into a compact configuration for convenience of storage and transport.
Another object of the present invention is to provide a low-cost binocular architecture that can be easily modified to provide a range of externally similar binoculars of different magnification.
Still another object of the present invention is to provide a series of optical designs for use in low-cost binoculars.
Yet another object of the present invention is to provide easily adjustable binocular designs that utilize four-mirror assemblies in each eye path for providing correct image orientation.
Other objects of the invention will be apparent and will appear hereinafter as will be evident from the following detailed description when read in connection with the accompanying drawings.